Crystal structure and associated local mechanical properties are considered to be among the factors determining the impact sensitivity of reactive chemicals. However, their contribution can hardly be separated from those stemming from the molecular structure per se (number and presence of explosophores, energy content). In this work, we analyzed a set of structurally diverse energetic compounds to look for possible correlations among the level of response toward impact stimulation (sensitivity), local mechanical properties, and crystal structure. In line with previous literature, a strong correlation with the energy content and impact sensitivity emerges, but the target safety property is also affected by the average elastic modulus of the crystal. Since the mechanical properties of crystalline materials are largely determined by the crystal structure, we investigate the rigidity and anisotropy of intermolecular interactions. We find that an increase in the anisotropy of the intermolecular interactions' network leads to a decrease in impact sensitivity. Our findings on the mechanical properties within a diverse data set of explosives and their correlations with the safety of materials might be used for prediction models and controlled design of future materials.

Early detection of the thermal and explosion hazards of chemicals is vital for safe handling and manufacturing. While thermal analysis methods using sealed-cell differential scanning calorimetry are commonly used to screen for shock sensitivity via empirical Yoshida-type equations, the reliability of the underlying thermal data and the robustness of this predictive approach require systematic validation. This study investigates the Yoshida approach from thermal analysis and energetic materials perspectives. We compiled a data set of more than 100 reactive compounds, including common reagents and energetic materials, to critically evaluate the variability of decomposition enthalpy and characteristic onset by DSC. Our results reveal significant scatter, up to several times, in reported decomposition heat values, attributable to factors such as gas leakage, calibration inconsistencies, interactions with crucible, and thermal runaway. We establish a correlation between decomposition enthalpy and the thermodynamically estimated maximal heat of explosion for the compound. Furthermore, by comparing original Yoshida and Pfizer-modified equations against experimental mechanical sensitivity data, we demonstrate that the conservative Pfizer adaptation achieves a superior recall (true positive rate) for identifying hazardous compounds. This work underscores the thermodynamic (energy content) and kinetic (onset temperature) foundations of the Yoshida-type equations, highlights the critical need for standardized, high-quality thermal data, and provides practical guidance for enhancing the reliability of early-stage hazard screening tools in chemical research and development.

Melting often accompanies the thermolysis of crystalline organic compounds and brings additional complexity for the thermokinetic analysis of the decomposition process. As a consequence of this, the kinetic data for the thermolysis of particular compounds both in the solid- and liquid-state are rarely reported and often contradict each other. Herein, we proposed a strategy of dealing with the melting with decomposition case for various types of thermoanalytical experiments (DSC and TGA) and temperature programs (both isothermal and non-isothermal). Furthermore, we proposed to study several related species differing by non-energetic moieties to shift the melting point over a wide temperature range without remarkable changes in the decomposition temperatures. To illustrate the value of the proposed approach, we consider the decomposition kinetics of the three halogenated benzene derivatives bearing a 2-nitrodiazene-1-N-oxide moiety. In all cases, the nonisothermal experimental data are fitted by a first-order reaction paralleled by the autocatalytic process. The isothermal experiments below the melting point of compounds in ramped heating runs still show the formation of liquid. This observation and other findings are explained using the Bawn kinetic model. The activation energies for the liquid-state decomposition of all compounds were found to be 145 ± 3 kJ mol-1. The experiment was complemented by the highly accurate CCSD(T)-F12 quantum chemical calculations. Theory predicts the primary decomposition pathway to be the radical scission of a nitro radical followed by the fast elimination of nitrous oxide. With the suggested approach, we determined the acceleration factor of the rate constant when decomposition commences in the solid or liquid state to be 2-4 times, not orders of magnitude, as was proposed in some previous publications.

Polynitro glycoluril derivatives, viz., 1,4-dinitroglycoluril (DINGU) and 1,3,4,6-tetranitroglycoluril (sorguyl, TNGU), are very promising components of energetic formulations because of their good detonation performance, high density, and low sensitivity to mechanical stimuli. However, the data available on the kinetics and mechanism of their thermal decomposition remain very limited. In the present contribution, we employed mutually complementing advanced experimental techniques (DSC and TGA in the solid state both under linear heating and isothermal conditions along with advanced thermokinetic models, optical microscopy, and gas product detection) and predictive quantum chemical calculations (DLPNO-CCSD(T)) to study the thermal stability of the title species. The experimental thermolysis data of DINGU and TNGU including both gravimetric (TGA) and caloric (DSC) datasets were used for building two-step kinetic models that universally describe all DSC and TGA data. More specifically, the first step for both nitroglycolurils is a nucleation-growth reaction described by the Kolmogorov-Johnson-Mehl-Avrami-Erofeev equation (KJMAE), while the second consecutive step obeys flexible Prout-Tompkins and third-order reaction models for DINGU and TNGU, respectively. The experimental findings were complemented by the mechanistic details from DLPNO-CCSD(T) quantum chemical calculations. The radical N-NO2 bond cleavage is the dominant primary decomposition channel with the kinetic parameters Ea = 185.8 kJ mol-1 and log(A/s-1) = 18.6 for DINGU, and Ea = 166.1 kJ mol-1 and log(A/s-1) = 18.7 for TNGU, respectively. Apart from the primary reactions, we also considered a number of uni- and bimolecular secondary decomposition channels. We found that the "bridge" C-C bond unzipping followed by the ˙NO2 radical elimination with activation barriers of ∼120-130 kJ mol-1 are the most energetically favorable unimolecular secondary channels. At the same time, the hydrogen abstraction from an initial reagent molecule by a primary nitramine radical product is the most important bimolecular secondary channel. The reaction mechanism switches from bimolecular to unimolecular C-C bond unzipping at the isokinetic temperatures of 860 K for DINGU and 610 K for TNGU. The reported secondary reactions might also be important in the thermolysis mechanisms of the related energetic secondary nitramines (e.g., RDX, HMX, and CL-20). Apart from this, we also determined a mutually consistent set of thermochemical and phase change data for a series of polynitro glycoluril derivatives.

Organic derivatives of hydroxylamine are important reagents in modern chemistry, but their thermal stability and related hazards have not yet been systematically studied. In the present study, we report a detailed thermal analysis of N-hydroxysuccinimide (NHS), N-hydroxyphthalimide (NHPI), 1,4-piperazine diol (PipzDiol), 1,3,5-trihydroxy-1,3,5-triazinan-1-ium chloride (formaldoxime trimer hydrochloride, TFOHCl), and tris-oxime TRISOXH3. Then, we suggest the effective kinetic parameters and mechanisms of thermal decomposition. All these NOH-containing chemicals exhibit the exothermic decomposition when examined under conditions that retard material vaporization (such as DSC at elevated pressure or in hermetic crucibles). The application of Yoshida-type rules points to a certain hazard associated with TFOHCl, TRISOXH3, and PipzDiol. Small-scale mechanical sensitivity testing validated the DSC-based hypothesis: TFOHCl explodes at certain drop energies, and two other species decompose under impact. The standard drop energies corresponding to 50% probability of initiation are within 14-26 J. Overall, the reactive chemistry of the analyzed hydroxylamines may result in certain risks when they are stimulated by temperature or impact. Even for well-known reagents such as NHS, the amount of heat liberated in the course of decomposition is considerable (about 1300 J g-1). 1,3,5-Trihydroxy-1,3,5-triazinan-1-ium chloride by the amount of decomposition enthalpy (2200 +/- 300 J g-1) and the level of the impact sensitivity (16 +/- 5 J) can be compared with explosives, but it is less thermally stable, decomposing above 100 degrees C. The calculation of virtual detonation performance of this salt shows much higher stored energy as compared to other studied hydroxylamines. We propose the calculation of the detonation parameters for screened compounds as an alternative way of explosive hazard identification.

Pyrazine 1,4-dioxide (PZDO) is a chemical frequently employed as a coformer in cocrystal design. It has two N-oxide fragments that signify potential hazards, but we found no information about it in prior literature. Therefore, we investigate the thermal behavior, thermochemical properties, and mechanical sensitivity of the title compound. We demonstrate that the material explodes in standard impact tests at a certain drop energy. By the level of its computed energetic potential, PZDO approaches benchmark trinitrotoluene. We screened ten energetic materials for cocrystal formation with PZDO using thermal analysis methods and predicted three novel cocrystals. However, we failed to grow the X-ray quality crystals by the conventional approach due to significantly differing solubility of PZDO and other components in common solvents. Two suitable coarse cocrystals of 3,4-dinitropyrazole/PZDO and 3,5-dinitropyrazole/PZDO were finally prepared by resublimation (vacuum recondensation of preformed comelt), and its X-ray structure is reported. Overall, we characterize PZDO as an energetic material and highlight the potential risks associated with the compound. The preparation of cocrystals via the gas phase route, although laborious, may be effective when the traditional (via solution) approach fails.

Energetic materials are important class of functional compounds that combine the beauty of extreme high-energy chemistry with rigorous constraints on safety and performance. As a result, the development of energetic materials is a challenging process that require the best of computational, chemical synthesis, and material design techniques. This review discusses the state-of-art of the energetics field, and then highlights the most recent synthetic advancements that go beyond – regioisomerism impact, almost all-nitrogen species, new mesoionic ring fragments, and compounds bearing elements other than traditional CHNO. The computational advancements are summarized further: the material genome approaches and high-throughput virtual screening. Next, the material science and crystal engineering design tools are reviewed, from cocrystal design and host-guest inclusion to various polymer coating techniques. Overall, we showcase the complexity of interdisciplinary problem of energetic materials design, that entraps the original mostly organic chemical field, but then material science and crystal engineering, and now targets the computational discovery and machine learning.

Nitrogen heterocyclic scaffolds retain their leading position as valuable building blocks in material science, particularly for the design of small-molecule energetic materials. However, the search for more balanced combinations of directly linked heterocyclic cores is far from being exhausted and aims to reach ideally balanced high-energy substances. Herein, we present the synthetic route to novel pyrazole-furoxan framework enriched with nitro groups and demonstrate a promising set of properties, viz., good thermal stability, acceptable mechanical sensitivity, and high detonation performance. In-depth crystal analysis showed that the isomers having lower-impact sensitivity values in both types of regioisomeric pairs are those with the exocyclic furoxan oxygen atom being closer to the pyrazole ring. Owing to the favorable combination of high crystal densities (1.83-1.93 g cm(-3)), positive oxygen balance to CO (up to +13.9%), and high enthalpies of formation (322-435 kJ mol(-1)), the synthesized compounds show high calculated detonation velocities (8.4-9.1 km s(-1)) and excellent metal accelerating abilities. The incorporation of the 3-nitrofuroxan moiety increases the thermal stability (by ca. 20 degrees C) and decreases the mechanical sensitivity of target hybrid materials in both types of regioisomeric pairs. Simultaneously, the detonation performance of 3-nitrofuroxans is almost identical to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric tunability in the future design of energetic materials.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Novel energetic materials (EM) often combine two intrinsically counter trends, viz., a high energy density and mediocre safety parameters, like thermal stability and sensitivity toward mechanical stimuli. A rational design of promising EMs requires a proper understanding of their thermal stability at both macroscopic and molecular levels. In the present contribution, we studied in detail the thermal stability of 4,4 '-dinitro-3,3 '-diazenofuroxan (DDF), an ultrahigh-performance energetic material with a reliable experimental detonation velocity being very close to 10 km s-1. To this end, we employed a set of complementary thermoanalytical (DSC and TGA in the solid state along with advanced thermokinetic models, optical microscopy, and gas products detection) and theoretical techniques (DLPNO-CCSD(T) quantum chemical calculations). According to the DSC measurements, the solid-state thermolysis of DDF turned out to be a complex three-step process. The decomposition commences at similar to 85 degrees C and the most intense heat release occurs at similar to 130 degrees C depending on the heating rate. In order to properly describe the kinetics of DDF thermolysis beyond the simple Kissinger and Friedman methods, we applied a "top-down" kinetic approach resulting in the formal model comprised of three independent stages. A flexible Kolmogorov-Johnson-Mehl-Avrami-Erofeev equation was applied for the first decomposition stage along with the extended Prout-Tompkins equation for the second and third processes, respectively. The formal exponent in the former equation turned out to be close to a second order, thus suggesting a two-dimensional nuclei-growth model for the first stage. We rationalized this fact with the aid of optical microscopy experiments tracking the changes in the morphology of a solid DDF sample. Then, we complemented the formal macroscopic kinetics with some mechanistic patterns of the primary decomposition channels from quantum chemical calculations. The three reactions involving all important moieties of the DDF molecule turned out to compete very closely: viz., the nitro-nitrite isomerization, radical C(heterocycle)-N(bridge) bond scission and molecular decomposition comprised of the consequent N-O and C-C bond scissions in a furoxane ring. The DLPNO-CCSD(T) activation barriers of all these reactions were close to similar to 230 kJ mol-1. Most importantly, the calculations provide some mechanistic details missing in thermoanalytical experiment and formal kinetic models. Apart from this, we also determined a mutually consistent set of thermochemical and phase change data for DDF.

While the effect of isomerism on the properties of energetic molecules has long been recognized, the use of this phenomenon to deliberately improve the performance of energetic materials has now been approached. Here, we report the development of effective protocols for the preparation of isomeric energetic compounds with a furazan-triazole-pyrazole framework, which differ in the binding points of these subunits and in the position of the nitro group. The two synthesized isomers readily form X-ray quality crystals of solvates with DMSO and water, but only one isomer was able to give unsolvated crystals. Significant differences in molecular geometry and noncovalent interactions due to the effect of the solvent incorporated into the crystal lattice are highlighted. The ambiguity of evaluating structure-property relationships for a single compound from the X-ray data of its solvate is demonstrated. The isomer synthesized for the first time, 3-(5-(5-(3,4-dinitro-1H-pyrazol-5-yl)-1H-1,2,4-triazol-3-yl)-4-nitrofurazan (6), is of greater interest because, unlike the other isomer, it is not hygroscopic and has a higher density. Isomer 6 has a shock sensitivity and detonation velocity similar to those of RDX, but it is more thermally stable and insensitive to friction.

Mechanical stress is an important trigger of reactions in chemicals. Historically, the standard testing protocols for impact and friction sensitivity have been developed mainly for energetic materials and explosives. As a result, the structure-mechanical safety data is available for common explosives and is constantly reported for newly synthesized energetic compounds. The present work is motivated by the widely held among practitioners idea of high variability of mechanical sensitivity data, the advancements of new heterocyclic and high-nitrogen chemistry, and clear need in benchmark reference data set for QSPR modeling. We started from literature analysis and have already noted that many chemical papers lack the details required to replicate their findings regarding mechanical sensitivity. Next, we prepared over 100 species that have been previously synthesized and whose sensitivity had been reported by other researchers. The scatter within the literature and present study's results is illustrated and analyzed. Finally, we proposed a data set of 83 chemicals, which have the most reliable mechanical sensitivity data. This benchmark data set is recommended to be used for modeling of mechanical hazards of reactive chemicals. The logics of how this data set can be expanded in future is given; it might involve the collaborative efforts by different groups.

Tetrazino-tetrazine 1,3,6,8-Tetraoxide (TTTO) is one of the most powerful energetic materials synthesized to date. Its thermal decomposition of [1,2,3,4]tetrazino[5,6-e][1,2,3,4]tetrazine 1,3,6,8-tetraoxide (TTTO) has been investigated for the first time. The obtained formal kinetic model of thermolysis includes the twodimensional nucleation-growth with an activation energy of 102 & PLUSMN; 3 kJ mol-1 and the second-order reaction with barrier of 184 & PLUSMN; 4 kJ mol-1. Judged by the decomposition onset (155 degrees C), TTTO is the most thermally stable among known top energetic substances. A broader analysis of 360 energetic and non-energetic chemicals supports the idea of general thermal stability decrease with the molecule's energy content rise, although the relationship is built as envelope of the cloud of experimental data. Two hypotheses for high energetic materials design are formulated: the limiting value of performance achieved with stable organic species (10% over benchmark 1,3,5,7-tetranitro-1,3,5,7-tetrazocane, HMX) and the existence of top performing molecules that are more thermally stable compounds than TTTO.

A number of new high-performing energetic materials possess explosophoric functionalities, high nitrogen content, and fused heterocyclic blocks. Two representatives of these materials have been synthesized recently, namely, 1,2,9,10-tetranitrodipyrazolo[1,5-d:5',1'-f][1,2,3,4]-tetrazine (1) and 2,9-dinitrobis([1,2,4]triazolo)[1,5-d:5',1'-f][1,2,3,4]tetrazine (2). The thermal stability of these energetic materials bearing the N-N-N = N-N-N fragment and three closely related compounds has been investigated for the first time. The thermal decomposition process of analyzed compounds was complicated by the appearance of the liquid phase, sublimation of the material, and autocatalysis by reaction products. In contrast to the traditional approach to the kinetic modeling based on data from either TGA or DSC, we use both signals' data measured at the same time and perform the joint kinetic analysis using the model-fitting technique to obtain the pertinent kinetic description of the process. Of the analyzed materials, 1 and 2 show the lowest thermal stability in melt with a characteristic rate constant of 2.6 × 10-3 s-1 at 250 °C. The kinetic parameters and calculated detonation performance data were used in the model to describe the mechanical sensitivity. The model output and the experimental friction sensitivity data show a respectable agreement, but more data are required to draw firm conclusions. In general, the provided thermal stability and kinetic data can be used for thermal response and storage modeling of these new N6-type energetic materials. The developed thermokinetic approach, joint model-fitting of several thermal analysis signals, can be applied to other complex thermally induced processes to increase the value and credibility of the kinetic findings.

Attention is called to numerous publications that have recently appeared in Biomass Conversion and Biorefinery and reported on the application of single heating rate methods to pyrolysis data. Emphasis is laid on the fact that these methods generally fail to determine trustworthy kinetics triplets, i.e., the reaction model, activation energy, and preexponential factor. The reasons and instances of the failure are briefly discussed and illustrated. It is stressed that the International Confederation for Thermal Analysis and Calorimetry recommends single heating rate methods to be avoided and the methods that use several heating rates simultaneously to be employed for reliable kinetic analyses.